JP2002098867A - Optical cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To harmonize the necessity of high power density for increasing Raman amplifier efficiency with that of low power density for reducing nonlinear operation in an optical transmission system. SOLUTION: The optical cable is characterized in that it has one or more single mode optical fibers of a first type and one or more optical fibers of a second type, that both types of optical fibers are suitable for transmitting optical signals at a system wavelength λs, and that the effective cross section of the first type optical fiber is substantially larger than that of the second type. In such a cable structure, it is desirable that the optical fiber of the large effective cross section (i.e., Aeff>=70 μm2) and that of the small effective cross section (i.e., Aeff<=60 μm2) are contained in the same numbers in the same cable. In addition, a variety of cable structure can contain, for example, a planar array of optical fibers bound together by a matrix material and a fiber group enclosed within one or more plastic tubes.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to information transmission using an optical fiber. More particularly, the invention relates to optical fiber design.

[0002]

2. Description of the Related Art Optical communications have made tremendous progress due to the ultra-wide bandwidth available in optical fibers. According to such bandwidth, thousands of phone conversations and TV channels,
It can be transmitted simultaneously through an optical fiber as thin as hair made of high quality glass material. Nevertheless, as with electrical signals, optical signals also suffer losses during transmission, so the need for amplification can be reduced by increasing the power of the optical signal to be transmitted, but still periodically Must be amplified. Fibers with large effective cross-sections have been developed to handle the nonlinear effects associated with high power densities when processing high optical powers.

[0003] Optical amplification is much more cost effective than converting an optical signal to an electrical signal, amplifying it, and then reconverting it to an optical signal. One example of an optical amplification method is
Doping a rare earth element such as erbium or praseodymium over the entire length of the optical fiber, pumping light energy over the entire length of the optical fiber at a wavelength different from the wavelength of the optical fiber to be amplified, and Propagates an optical signal along with and extracts energy at the frequency of the signal itself. Using an optical fiber doped with erbium, (Er ³⁺
Amplify an optical signal having a wavelength of 1550 nm (where the dopant ions transition). On the other hand, Praseodymium is 1310
Useful in the nm range. While such amplifiers provide much better improvements than conventional electronic amplification methods, the cost of such optical amplifiers is very high. For example, $ 25,
000 to $ 50,000. In addition, erbium amplifiers must be driven by one or two laser diode pumps. Thus, when the excitation stops, all systems go down. (Erbium does not penetrate transparently, but erbium uses a pre-level laser to absorb the signal as it attenuates.) Praseodymium amplifiers have roughly the same problems, but in addition, It is made of a friable fiber that is fragile and fragile.

[0004] Another optical amplification method is stimulated Raman scattering (SR).
Utilize a phenomenon known as S). A useful advantage of this optical amplification method is low cost (e.g., $ 3000-
$ 4000), operability at all wavelengths, use of the transparent fiber itself for amplification, etc. In fact, this method relies on the intrinsic properties of the fiber material and does not require that special dopants, such as erbium, be present in the fiber. Therefore, it is highly desirable to use Raman amplification in optical transmission systems.

[0005]

Raman amplification involves the introduction of an optical excitation signal into the transmission medium. Also, for a given pump power, the Raman amplification efficiency increases as the optical power density increases. However, if the power density of the fiber becomes too large, the optical transmission signal experiences undesirable nonlinear effects. Therefore, it is desirable to balance the need for high power density to increase Raman amplifier efficiency in optical transmission systems with the need for low power density to reduce nonlinear effects.

[0006]

SUMMARY OF THE INVENTION The object comprises one or more single mode optical fibers of a first type and one or more optical fibers of a second type, both types of optical fibers. both are suitable for transmitting optical signals in a system wavelength lambda _s, the effective cross-sectional area of the first type of optical fiber is characterized by substantially greater than the effective cross-sectional area of the second type of optical fiber It is solved by the cable of the invention.

[0007] Various cable configurations are shown according to exemplary embodiments of the present invention. In such a cable structure, it is preferable to include the same number of large effective area fibers (ie, A _eff ≧ 70 μm ² ) and small effective area fibers (ie, A _eff ≦ 60 μm ² ) in the same cable. . Further, various cable structures may include a planar array tied together by a matrix material and a group of fibers encapsulated in one or more plastic tubes.

In an exemplary embodiment of the invention, the optical cable is deployed in a Raman amplified optical transmission system where an optical transmission signal is connected to one end of an optical fiber of a first type. The other end of the fiber is connected to a second type of optical fiber. The optical excitation signal is coupled to a second optical fiber. The optical excitation signal causes stimulated Raman scattering in the second optical fiber, thereby causing amplification of the optical transmission signal. Preferably, the optical excitation signal propagates along the second optical fiber in a direction opposite to the direction of the optical transmission signal.

[0009]

DETAILED DESCRIPTION OF THE INVENTION Terminology The terms commonly used by those skilled in the art are defined as follows. (1) Effective area (A _eff ) This is an optical attribute specified for a single mode optical fiber, and is defined by the following equation. A _eff = 2π (∫ ₀ ^∞ E ² rdr) ² / (∫ ₀ ^∞ E ⁴ rdr) (where E is the electric field associated with the propagated light) In practice, the effective area is Of the mode field diameter of the fiber according to the mapping function of A _eff = kπ (MFD / 2) ² (where k is a fitting coefficient) (2) Mode field diameter (MFD) A measure of the width of the guided light power intensity in a single mode fiber. For most single mode fibers, the shape of the intensity versus radius position will generally be a regular Gaussian or bell-shaped curve. The radius at which the intensity drops to the 1 / e ² = 0.135 peak value is called the mode field radius. If this radius is doubled, an MFD is obtained. (3) Large effective area For the purposes of the present invention, an optical fiber with A _eff ≧ 70 μm ² . (4) Small effective area For the purposes of the present invention, an optical fiber where A _eff ≦ 60 μm ² . (5) Stimulated Raman scattering (SRS) Interaction between light and molecular vibrations of an optical fiber. (6) System wavelength (λ _s ) The center wavelength of a single optical channel or the average center wavelength of a group of optical channels present in the amplification band of an optical amplifier.

[0010] If a single cable contains all the different types of fibers required in a particular transmission system, optical fiber manufacturers and wiring contractors benefit. The present invention is an optical fiber that can be advantageously used in a Raman pump light transmission system. Such pumping allows the optical fiber to provide a small amount of amplification. This is often augmented by auxiliary optical amplifiers. By using both large and small effective area fibers with Raman amplifiers, longer transmission spans are possible before auxiliary amplifiers are needed. Also, if a single cable contains both large and small effective area fibers, inventory is reduced and wiring implementation is simplified. An outline of the effective area of the fiber and Raman amplification will be described.

Effective Area of Fiber As described above, the effective area is an optical attribute specified for a single mode optical fiber and is defined by the following equation: _{^{(4 rdr ∫ 0 ∞ E)}} ( wherein, E is an electric field associated with light _{propagated.) A eff = 2π (∫} 0 ∞ E 2 rdr) 2 / In practice, the effective cross-sectional area, the mapping It is related to the mode field diameter of the fiber as a function of function. The mapping function uses the measurement of one attribute to predict the value of another attribute for a given fiber. For a given fiber type and design, the MFD can be used to predict the effective area by a mapping function that is specific to a particular fiber type and design. The mapping function is generated by repeating an experiment. In this experiment, a sample of fiber that represents a spectrum of both MFD and fiber type values is selected, and the fiber in this sample is measured for both MFD and _Aeff . Linear regression can be used to determine fitting coefficients. It is defined by the following equation: A _eff = kπ (MFD / 2) ² The measurement of the effective area of a single-mode optical fiber is calculated by TIA /
This is described in detail in FTOP-132, which is to be published as EIA-455-132-A.

It is well known that a nonlinear interaction (NLI) between an optical signal and a propagation medium (eg, an optical fiber) can be used in principle for amplification of Raman amplifier signal radiation. Optical fiber N
LI amplifiers take advantage of the intrinsic properties of the fiber material and do not require that certain dopants, such as erbium, be present in the fiber. When transmitting multiple wavelengths on a single optical fiber, there are several non-linear mechanisms that can transmit signal energy between wavelengths. SRS
Is the nonlinear parametric interaction between light and molecular vibration. Light launched into the optical fiber is partially scattered and downshifted in frequency. The change in optical frequency is
Corresponds to molecular vibration frequency. SRS is similar to stimulated Brillouin scattering (SBS), but can occur in either the forward or reverse direction. The Raman gain coefficient is about three orders of magnitude smaller than the Brillouin gain coefficient. Thus, in a single channel system, the SRS threshold is about three orders of magnitude greater than the SBS threshold. However, 12 THz or 120 nm
The gain bandwidth of the SRS is much larger than the gain bandwidth of the SBS. For a more detailed description of SRS, see Optical Fi
ber Transmission Systems Using Stimulated Raman Sc
attering: Theory, by Kiyofumi Mochizuki, Journal o
f Lightwave Technology, Vol.LT-3, No.3, June 1985
It is described in.

FIG. 1 is a schematic configuration diagram of an optical transmission system 100 that uses an SRS for amplification. The transmitter 10 generates, for example, an optical transmission signal (λ _s ) in a wavelength region of 1550 nm. This signal is sent to optical fiber 1 before amplification is required.
It travels distances of tens of kilometers along 1 and 12. Raman amplification is an optical pump signal (λ _p ) having a wavelength different from λ _s
Is introduced into the transmission fiber 12 via the wavelength division multiplexer (WDM) 15. Preferably, the optical excitation signal is transmitted in a direction opposite to the signal propagation direction. This is therefore known as "reverse pumping". As described in U.S. patent application Ser. No. 08 / 683,044, reverse pumping is preferred over forward pumping. This is because reverse pumping greatly reduces the crosstalk associated with excitation depletion modulation. Nevertheless, forward pumping of the optical fiber 12 is also contemplated in an optical transmission system according to the present invention.

Amplification in the fiber by the Raman effect is possible when the wavelength separation between the optical pump signal λ _p and the optical transmission signal λ _s has been performed accurately. In the case of a fused silica fiber, when a sufficient pumping power (30 mW or more) is applied, remarkable Raman amplification is performed over a relatively wide frequency band. The amount of Raman gain obtained is directly proportional to the amount of pump power applied to the fiber.

FIG. 2 shows the Raman gain factor of a fused silica fiber as a function of the channel separation between the excitation and transmission signals, expressed in units of THz and cm ⁻¹ , the units of measurement used in the spectrometer. FIG. The Raman gain factor shown in FIG. 2 applies to an optical transmission wavelength of about 1.55 μm and a matching signal polarization of the pump and transmission signals. For scrambled polarization, this factor is reduced to about half the value shown. The gain curve peaks when the excitation frequency is about 12 THz (400 cm ^-1 ), which is lower than the transmission frequency. The gain factor at this peak is about 7
× 10 ⁻¹² cm / W. S in optical transmission system
The longer wavelength signal from the RS is amplified by the shorter wavelength signal. While there is a significant decrease above 120 nm, SRS combines channels separated at wavelengths up to 140 nm or less. For an optical transmission signal propagating in the 1.55 μm region, this means that
All signals having a wavelength between 50 nm mean that energy can be transferred to the optical signal, as shown in FIG.

In a preferred embodiment of the present invention, 1429
Excitation signals having wavelengths of nm, 1446 nm, 1470 nm and 1491 nm are used simultaneously to provide a wide and flat band of Raman amplification to the wavelength division multiplexed optical transmission signal. Each excitation signal has a different power level. The accumulated power is about 600 mW. Further, the Raman amplifier can be driven by multiple laser diodes for continuous use. If one laser diode stops operating, the other laser diode will continue to provide amplification power to the fiber.

In one direction, WDM 15 routes signals from a single input port to multiple output ports according to wavelength, and in another direction, a single signal of different wavelengths from multiple input ports. Route to the output port of Accordingly, the optical transmission signal λ _s is routed from the fiber 12 toward the receiver 20 and the optical pump signal λ _p is routed from the Raman amplifier 16 toward the fiber 12. According to the present invention, the optical fibers 11 and 12 are each different, the optical fiber 11 is selected to be compatible with optical transmission signals having high intensity, and the optical fiber 12 is selected to enhance Raman amplification in an efficient manner. Is done.

Raman amplification is enhanced by high power density
Is a non-linear action. This is the field for a given pump power.
Molecules reduce the effective cross-sectional area of the optical fiber that causes amplification.
It means that the amplification is enhanced by reducing the amount.
This is clearly illustrated in FIG. FIG.
Using Raman amplification for optical fiber with effective cross section
The relationship between optical power and distance in an optical transmission system
FIG. Optical transmission signal at distance "0km"
Is launched into the optical fiber at a distance of
0 km "applies to the fiber. Curve 301
-304 is an optical transmission path as a function of distance from the launch site.
FIG. 4 is a graph showing how power is reduced. Song
Line 304 shows the system without Raman amplification, curve 3
01-303 is a system to which Raman pumping is applied
About. Amplification is a function of the effective area of the fiber
Such pumping, which varies inversely,
Is done. The smaller the effective area, the greater the amplification
It will be good. Curve 301 is A _eff= 55 μm^TwoIs the light fa
Show Iva. Curve 302 is A_eff= 72 μm^TwoThe light
Indicates a fiber. Curve 303 is A_eff= 82 μm^TwoIs the light
2 shows a fiber.

Advantageously, the optical signal to noise ratio (OS
NR) also varies inversely as a function of the effective area of the fiber. As shown in FIG. 4, the smaller the effective area, the larger the OSNR. FIG. 4 is a graph showing an optical signal-to-noise ratio in Raman amplification of optical fibers having different effective areas. Curve 401 shows an optical fiber where A _eff = 55 μm ² . Curve 402
Indicates an optical fiber in which A _eff = 72 μm ² . Curve 40
Reference numeral 3 denotes an optical fiber where A _eff = 82 μm ² . Therefore, when Raman amplification is desired, it is very effective to use an optical fiber having a small effective area.

On the other hand, an optical fiber having a large effective area allows a greater signal power to be applied to the fiber before the nonlinear action is performed. High signal power is clearly desirable. This is because this high signal power allows the optical signal to propagate further away before amplification is required. Obviously, both large and small effective area fibers are desirable in optical transmission systems where Raman amplification is to be used. In a preferred embodiment of the present invention, both the large effective area fiber and the small effective area fiber are contained in a single cable, as shown in FIG. As shown in FIG. 5, a plurality of fiber bundles 50-1 and 50-2 are provided in a sturdy optical cable structure 500. In this figure, the fiber bundle 50-1 is composed of, for example, a group of optical fibers having a large effective area, and the fiber bundle 50-2 is composed of a group of optical fibers having a small effective area. Cable 500 can include various types of fiber bundles. What is important is that the cable include a plurality of fibers having a large effective area and a plurality of fibers having a small effective area.

FIG. 5 further details a practical cable structure according to the invention. The optical cable 500 is a fiber bundle 5 integrated as a unit by a binding yarn 51.
0-1, 50-2. The binding yarn 51 is generally
Colored for identification purposes. These fiber bundles are arranged in a tubular member 52. This tubular member 52
Is formed from a plastic material such as, for example, polyvinyl chloride or polyethylene. In some cases,
A gel-like filler can be used to fill the interior region of the tubular member 52, prevent water from entering, and serve as a protective buffer for the fiber. Around the tubular member 52 is a water absorbing tape 53 and an outer jacket 55 made of, for example, a polyethylene material. A reinforcing member 54 is provided between the water absorbing tape 53 and the outer jacket 55. These reinforcing members are made of metal or dielectric and are used to protect the optical fiber from tensile and / or compressive stress. This tensile and / or compressive stress is applied to the cable during handling and in normal use of the cable. A more detailed description of the structure of the cable 500 and suitable fillers is provided in U.S. Patent No. 4,844,575. This same general cable structure can be used if the fiber bundle is replaced by a ribbon as shown in FIG.

FIG. 6 shows a cable 600 consisting of a planar array of optical fibers disposed in a matrix material. Such cables are often called "ribbons". Here, eight optical fibers are shown divided into two groups 60-1 and 60-2. For example, group 60
-1 is composed of four optical fibers having a large effective area, and the group 60-2 is composed of four optical fibers having a small effective area. For ease of identification, each individual optical fiber is colored differently. Further, the ribbon 60
The 0 may also have a marking to identify which fibers have positive dispersion and which fibers have negative dispersion. For example, the brightly colored portion 61 of the ribbon 600 contains fibers with a large effective area and the ribbon 6
The dark colored portion 62 of 00 contains fibers of small effective area. In practicing the present invention, it is not always necessary to include the same number of fibers having a large effective area and the same number of fibers having a small effective area in the same cable, but preferably the same number. Further, by manufacturing ribbons that contain the same number of large effective area fibers and small effective area fibers, only one type of ribbon need be manufactured.

In a preferred embodiment of the present invention, the ribbon 6
00 comprises a parallel coplanar array of longitudinally extending optical fibers. Each optical fiber is encapsulated in an inner layer of paint and a photo-side layer and is provided with a colored identifier. Matrix coupling material 65 fills the gaps between the optical fibers and couples the optical fibers together into a single unit. Bonding material 65
Has an elastic modulus γ. This value is lower than the modulus of the outer coating of the fiber and higher than the modulus of the inner coating (ie, 10 ⁹ Pa>γ> 10 ⁶ Pa). This allows for some convenient fiber-to-fiber movement. Suitable binders are described in U.S. Pat. No. 4,900,126.

As described above, for transmission of a high-power optical signal, it is desirable to use a fiber having a large effective area because the power density and the nonlinearity are reduced. Conversely, small effective area fibers are desirable at the fiber locations where Raman pumping is introduced. This is because amplification increases when the power density of the excitation energy increases. These two apparently conflicting needs are solved by using a large effective area fiber where the signal energy is high and using a small effective area fiber where the signal energy is low along reverse Raman pumping. Therefore, it is necessary to interconnect large effective area fibers and small effective area fibers at a certain point (intersection). Such an interconnect is shown in FIG. The large effective area fiber 60-1 is connected to the small effective area fiber 60-2 via the connection 75. Such connections can be made by known and conventional fiber interconnections. Such a connection is, for example, Stephen C. Mettler et a
l. in "Optical Fiber Splicing," Optical Fiber Tele
communications II, (Stewart E. Miller at al. editor
s, 1988), pp. 263-300. The light-colored portion 61 of one ribbon 600 and the dark-colored portion 6 of another ribbon 600
Preferably, connection 2 is made at the midpoint of the cable span.

Since optical transmission systems are generally bidirectional, it is generally convenient to cross at an intermediate point between the amplifiers. As such, the non-linearities associated with excess optical power density are equal in both directions. Further, since the interconnected fibers are of inverse dispersion sign, the fiber 50-
Assuming that the positive dispersion provided by 1 is equal to the negative dispersion provided by fiber 50-2, the cumulative dispersion can be reduced to nearly zero. Other factors that affect the intersection location include the magnitude, slope and sign of the fiber dispersion, as well as the power levels of the excitation and optical signals.

Raman amplified optical transmission system 8 according to the present invention
An example of 0 is shown in FIG. In this embodiment, system 8
0 operates at 10 Gb / s in each direction and also has a light source, not shown. This light source is 1530-15
A large number of wavelength division multiplexed channels λ _1.
Generate λ _n . Each channel is separated by about 1.6 nm and each channel operates at a rate of about 2.5 Gb / s. Amplifiers 81-84 are 1530-156
An erbium-doped fiber amplifier (EDFA) that provides effective amplification in the 5 nm range. The power level of the optical transmission signal at the output of these amplifiers is sufficiently high. This power level desirably uses a large effective area fiber. Thus, in the right direction from the left, multi-channel via an amplifier 81, a large-effective-area fiber in the cable 500-1 extending over a length L ₁ 50-
Fired into 1. At this point, the multiplexed optical transmission signal λ ₁
The power level of λ _n is reduced to a level where the use of large effective area fibers is no longer required. For a single mode fiber, the power reduction rate is, for example, about 0.2 dB / km. A cross-splice connection 85 is then formed in the small effective area fiber 50-2 extending over the length L2, preferably at the mid-span. Cables 500-1 and 500-2 are identical to each other and are cables as shown in FIG. 5 including both large effective area fibers and small effective area fibers. Advantageously, the cable can be cut at any convenient point to form a splice connection.

The continuously from left to right, a wavelength division multiplexer (WDM) 87 is an optical transmission signal λ ₁ ··· λ _n E
The optical pump signal from the Raman amplifier 88 is directed to the optical fiber 50-2 in the reverse transmission direction. The optical excitation signal can be launched into fiber 50-2 from any or both directions, and at any point along the length of fiber 50-2. Optical transmission system 80
Operates similarly from right to left, and the cable 500-1
The optical fiber 50-2 is pumped back through the Raman amplifier 89 and the WDM 86 in the manner described above to perform amplification. The EDFAs 81-84 also require an optical excitation energy source (not shown), and although not required for the present invention, the EDFAs operate conveniently with amplification provided by stimulated Raman scattering in the fiber 50-2. Typical specifications of the fiber 50-1 and the fiber 50-2 are shown below.

Large effective area fiber specification Attenuation at 1550 nm 0.17 dB / km Mode field diameter at 1550 nm 11.8 μm Cladding layer diameter 125 ± 1.0 μm Cutoff frequency <1450 nm (2 m reference length) Dispersion at 1550 nm 21.5 ps / nm · km Relative dispersion gradient 0.0030 nm ^-1 Effective area 110 μm ² Coating diameter 245 ± 10 μm Yield test 100 kspi

Small effective area fiber specification Attenuation at 1550 nm 0.23 dB / km Mode field diameter at 1550 nm 6.9 μm Cladding layer diameter 125 ± 1.0 μm Cutoff frequency <1450 nm (2 m reference length) Dispersion at 1550 nm −17.7 ps / Nm · km Relative dispersion gradient 0.0033nm ^-1 Effective area 35μm ² Coating diameter 245 ± 10μm Yield test 100kspi

The fiber is a Raman amplification optical transmission system.
Although it is preferable to use them together with the system, for example, in the present invention,
Different effective area, different dispersion mark, suitable for use
And other fibers with different dispersion gradients
Also available from Lucent Technologies and Corning, Inc.
Have been. In fact, field workers have various system designs
In order to solve the problem, large effective area fiber and small effective area
Easy selection of any combination with cross-section fiber
Can be. The various specific embodiments of the present invention have been described above.
Has been described, but the specific article described in the above embodiment is
The matter can be changed as appropriate. For example, the optical transmission of the present invention
Light source wavelength (λ _s) Is 1530n
m can be outside the wavelength range of 1565 nm
The connection is made at a point other than the middle span (ie, L₁≠ L_Two)so
It is possible to use a different number of fibers with a small effective area fiber.
Using cables with large effective area fibers
Large effective area of different size at light source wavelength
And a cable containing a fiber with a small effective area
Can be used for large effective area fiber and small effective area
Cable with additional fiber in addition to area fiber
Can also be used, and also illustrated in the above embodiment.
Cable with a different structure from the
Optical cables without materials or reinforcing members)
Can also.

[0031]

As described above, according to the present invention,
The need for high power density to increase Raman amplifier efficiency in optical transmission systems can be balanced with the need for low power density to reduce nonlinear effects. That is, for transmission of a high power optical signal, it is desirable to use a fiber having a large effective area because the power density and the nonlinearity are reduced. Conversely, small effective area fibers are desirable at the fiber locations where Raman pumping is introduced. This is because amplification increases when the power density of the excitation energy increases. These two apparently conflicting needs are solved by using a large effective area fiber where the signal energy is high and using a small effective area fiber where the signal energy is low along reverse Raman pumping. Therefore, if a large effective area fiber and a small effective area fiber are interconnected at a certain point (intersection), the effect of the present invention can be obtained.

In the claims, the numbers in parentheses after the constituent elements of the invention are for making the invention easier to understand by associating the constituent elements with the embodiments. It should not be used for interpretation.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an optical transmission system using inverse pump Raman amplification.

FIG. 2: THz and c, the units of measurement used in the spectrometer
FIG. 4 is a graph illustrating the Raman gain factor of a fused silica fiber as a function of channel separation between the excitation signal and the transmission signal, expressed in units of m ⁻¹ .

FIG. 3 is a graph showing a relationship between optical power and distance in an optical transmission system using Raman amplification for optical fibers having different effective cross-sectional areas.

FIG. 4 is a graph showing an optical signal-to-noise ratio in Raman amplification of optical fibers having different effective areas.

FIG. 5 is a perspective view of a cable containing optical fiber bundles having different effective areas according to the present invention.

FIG. 6 is a perspective view of a cable containing a planar array of optical fibers having different effective areas according to the present invention.

FIG. 7 is a perspective view showing an example of interconnection by fusion splicing between optical fibers of the type shown in FIG.

8 is a block diagram using an optical cable as shown in FIG. 5 in an optical transmission system having both an erbium amplifier and a Raman amplifier.

[Explanation of symbols]

Reference Signs List 10 transmitter 11, 12 optical fiber 15 wavelength division multiplexer (WDM) 16 Raman amplifier 20 receiver 50-1, 50-2 optical fiber bundle 51 binding thread 52 tubular member 53 water absorbing tape 54 reinforcing member 55 outer jacket 60-1, Reference Signs List 60-2 Fiber group 61 Light color portion 62 Dark color portion 65 Matrix coupling member 75 Connection 80 Raman amplification optical transmission system 81, 82, 83, 84 Erbium-doped fiber amplifier (EDFA) 85 Cross splice 87 Wavelength division multiplexer (WDM) 88 Raman amplifier 100 Optical transmission system 500,600 Optical cable

 ──────────────────────────────────────────────────続 き Continuation of the front page (71) Applicant 596077259 600 Mountain Avenue, Murray Hill, New Jersey 07974-0636 U.S.A. S. A. (72) Inventor Arthur F. Judy Morningside Drive, Atlanta, Georgia, 30306 United States of America 1461 NF term (reference) 2H001 BB04 BB15 BB19 BB21 KK02 PP01 2H050 AB03Z AC13 AC38 AD01

Claims (9)

[Claims] 1. One or more single mode optical fibers (50-1, 60-1) of a first type and one or more optical fibers (50-2, 60-2) of a second type. Consisting of
Optical cables (500, 600), both types of optical fiber, suitable for transmitting optical signals of light source wavelength λ _s
The optical cable according to claim 1, wherein the first type of optical fiber has an effective area that is considerably larger than the effective area of the second type of optical fiber. 2. The optical fiber of the first type (50-
The effective area of 1) is A _eff ≧ 70 μm ² , and the effective area of the second type of optical fiber (50-2) is A
The optical cable (500) according to claim 1, wherein _eff ≦ 60 μm ² . 3. The optical fiber of the first type (50-
The optical cable (500) of claim 1, wherein 1) has a positive dispersion at 1550 nm and the second type of optical fiber (50-2) has a negative dispersion at 1550 nm. 4. The cable comprises: (a) a plastic tubular member (52) for enclosing the first and second types of optical fibers; and (b) a plastic jacket (enclosed) for enclosing the tubular member. 55. The optical cable (500) of claim 1, further comprising: (c) one or more reinforcing members (54) disposed within the cable. 5. The optical fiber of the first type (50-
The optical cable (500) according to claim 1, wherein 1) and the second type of optical fiber (50-2) have the same number, respectively. 6. The first type of optical fiber (60-
1) and the second type of optical fiber (60-2)
The optical cable (600) of claim 1, wherein the optical fibers are coupled together as a planar array, the optical fibers having longitudinal axes that are generally parallel to one another. 7. The cable comprises: (a) a plastic tubular member enclosing the planar array; (b) a plastic jacket enclosing the tubular member; and (c) disposed within the cable. The optical cable (600) of claim 6, further comprising one or more reinforcing members provided. 8. The optical fiber of the first type (50-
1) is assembled together in the first unit, and
The optical fiber of the second type (50-2) is wound together with a binder (51) and assembled together in a second unit and wound with a binder. The optical cable (5
00). 9. The cable comprises: (a) a plastic tubular member (52) for enclosing the first and second units; and (b) a plastic jacket (55) for enclosing the tubular member. The optical cable (500) according to claim 1, further comprising: (c) one or more reinforcing members (54) disposed within the cable.